1. Field of the Invention
The invention relates to an optical touch device and a touch sensing method and, more particularly, to an optical touch device having two image sensing units disposed at two corners of an indication plane diagonal to each other, respectively, and a touch sensing method adapted to the optical touch device.
2. Description of the Prior Art
Since consumer electronic products have become more and more lighter, thinner, shorter, and smaller, there is no space on these products for containing a conventional input device, such as mouse, keyboard, etc. With development of touch technology, in various kinds of consumer electronic products (e.g. display device, all-in-one device, mobile phone, personal digital assistant (PDA), etc.), a touch device has become a main tool for data input. Compared with other touch designs, such as a resistive touch design, a capacitive touch design, an ultrasonic touch design, or a projective touch design, an optical touch design has lower cost and is easier to use, especially for large-size touch display.
A conventional optical touch device senses a touch point indicated by a touch object (e.g. finger or stylus) on an indication plane by two image sensing modules arranged separately using a light-shielding manner or a light-reflecting manner. When the image sensing modules sense the touch object, a processing unit of the optical touch device can calculate the touch point indicated by the touch object accordingly.
Referring to FIGS. 1 and 2, FIG. 1 is a schematic diagram illustrating a light-reflecting type optical touch device 1 of the prior art, and FIG. 2 is a light-shielding type optical touch device 1′ of the prior art. As shown in FIG. 1, the optical touch device 1 comprises an indication plane 10, two image sensing units 12, a processing unit 14 and two light emitting units 16. The processing unit 14 is electrically connected to the two image sensing units 12. The two image sensing units 12 are disposed at two opposite corners of the same side of the indication plane 10. The two light emitting units 16 are disposed adjacent to the two image sensing units 12, respectively. As shown in FIG. 2, the main difference between the optical touch device 1′ and the aforesaid optical touch device 1 is that the optical touch device 1′ replaces the light emitting units 16 adjacent to the image sensing units 12 by a plurality of light emitting units 16 (e.g. light emitting frames) disposed around the indication plane 10.
When the optical touch device 1 or the optical touch device 1′ is used for sensing one single touch point performed by one single finger, the position of the touch point can be calculated by a triangulation method easily. However, once there are multiple touch points performed by two or more than two fingers, it is complicated for the processing unit 14 to identify and calculate positions of the touch points and this could result in mis-identification and interference. Ghost points are one problem for example. As shown in FIGS. 1 and 2, when two touch objects (e.g. two fingers) touches the indication plane 10 simultaneously, two touch points RP1, RP2 and two ghost points GP1, GP2 will be generated by images captured by the two image sensing units 12. At this time, the processing unit 14 will calculate coordinates of the two touch points RP1, RP2 and coordinates of the two ghost points GP1, GP2 according to the images sensed by the two image sensing units 12. Afterward, the processing unit 14 identifies the two touch points RP1, RP2 as real touch points by some characteristics and conditions and then outputs the coordinates of the two touch points RP1, RP2 after identification. The appearance of ghost points GP1, GP2 will increase complication and difficulty in identifying touch points and algorithm thereof so that the probability of mis-identification will increase in the optical touch device when sensing two or more than two touch points.